Interstitial cystitis (IC) is an inflammatory bladder condition with unknown etiology, although a defect in bladder cytoprotection by the urothelium and a pathophysiologic role for the mast cell has been implicated. We hypothesize that these two processes participate in a vicious cycle of inflammation, with tryptase released from activated mast cells activating the protease-activated receptor-2 (PAR-2) on urothelial and endothelial cells in the bladder and resulting in increased phospholipase A2 (PLA2) activity and accelerated production of inflammatory phospholipid metabolites such as eicosanoids and platelet activating factor (PAF). Additionally, mast cell tryptase may contribute to exacerbation of inflammation directly or indirectly by increasing the permeability of the urothelium leading to increased movement of urinary contents into the bladder wall and by increasing endothelial cell permeability and adhesion of polymorphonuclear leukocytes (PMNs) to the endothelium, resulting in increased PMN content in the bladder wall. The specific aims to test this hypothesis are: 1. To determine whether tryptase stimulation of human urothelial (HUR) cells contributes to the propagation of the inflammatory process by increasing PLA2 activity and production of inflammatory mediators, such as eicosanoids and PAF. Changes in urothelial cell permeability and resistance and the rate of wound healing in the urothelium will also be measured in the presence and absence of tryptase to determine the effect of tryptase on the barrier function of the urothelium. 2. To determine whether tryptase stimulation of human bladder microvascular endothelial cells contributes to the propagation of the inflammatory process by measuring PLA2 activity and phospholipid-derived inflammatory mediators in response to tryptase. Endothelial cell permeability, increased expression of cell surface adhesion molecules and increased PMN adherence to the endothelial cell monolayer will determine if tryptase contributes to PMN recruitment to the bladder. These studies will provide an understanding of the role of mast cells in the propagation of inflammation in the bladder in such conditions as IC and highlight possible avenues for pharmacological intervention to alleviate the debilitating symptoms of this disease.